1. Field of Invention
This invention relates generally to a sheet feeder for an image forming engine of an image forming apparatus.
2. Description of Related Art
To supply image recording media, generally referred to as "sheets", to the image forming engine, individual copy sheets are acquired from the top of a stack and are transported forward by a translating vacuum feed head into a set of take away nip rolls. Sheet fluffers separate a sheet from the top of the stack. The translating vacuum feed head acquires the separated sheet and feeds the separated sheet into the set of take-away nip rolls. The time for the translating vacuum feed head to acquire the sheet is relatively short. The height of the stack must be monitored and adjusted during sheet feeding to maintain the sheet acquisition time as short as possible. The stack height must also be monitored and adjusted to correct for problems caused, for example, by edge welding and/or poor separation between sheets. Current stack height monitoring methods rely on contact with the stack. This may cause marking of the sheets or reduction in the fluffing of the stack. Optical sensors are also currently used to monitor stack height. The optical sensors, however, may not be reliable when looking at the edge or top of a fluffed stack.